There is a growing need for personal protective apparel that guards against toxic chemical and biological agents. These agents may be                (a) accidentally released in a chemical manufacturing plant, in a scientific or medical laboratory or in a hospital;        (b) released intentionally during wartime by a government to attack the military forces of the opposition; or        (c) released during peacetime by criminal or terrorist organizations with the purpose of creating mayhem, fear and widespread destruction.        
For this reason, the United States military and other defense organizations of countries all over the world have sought to provide adequate protection against chemical and biological warfare agents. The need for such protective apparel also extends to police departments, fire departments, emergency responders and health care providers. These organizations are responsible for providing assistance and relief after a catastrophic release of chemical or biological toxins, but they cannot discharge their responsibilities without adequate protection (“Chemical Protective Clothing for Law Enforcement Patrol Officers and Emergency Medical Services when Responding to Terrorism with Chemical Weapons”, Arca, V. J. and Marshall, S. M., in report of the Chemical Weapons, Improved Response Program, U.S. Army Soldier and Biological Chemical Command, November 1999).
According to the Handbook of Chemical and Biological Warfare Agents (D. Hank Ellison, CRC Press, Boca Raton, Fla., 1st edition, 1999), most chemical warfare toxins are fatal at concentrations as low as 1 part per million (ppm). Hence, to provide adequate protection from chemical warfare agents, a protective suit has to be almost impermeable to such chemicals. It is not difficult to devise structures that are impermeable to toxic chemical vapors and liquids, but such structures are also hot, heavy and uncomfortable to wear. The degree of comfort offered by a protective suit is largely determined by the amount of water vapor that can permeate through the protective fabric. The human body continuously perspires water vapor as a method for controlling body temperature. When a protective fabric hinders the loss of water vapor from the body, the transpirational cooling process is hindered, which leads to personal discomfort. When a protective suit allows little or no loss of water vapor, extreme heat stress or heat stroke can result in a short period of time. Hence, in addition to offering the highest levels of protection against toxic chemicals and liquids, it is desirable that a practical chemical and biological protective suit have high water vapor transmission rates. Desirable protective structures are also light in weight and offer the same high level of protection over a long period of time.
Some currently available protective garments offer a constant level of protection at all times, but in most situations, protection is only needed when a toxic chemical or biological agent is present in the environment. Further, comfort is typically sacrificed at the expense of protection or vice versa. A garment is needed that provides a variable and controllable permeability.
U.S. application Ser. No. 11/118,961 discloses a structure having two membranes and means to respond to an actuating stimulus (for example, an electrostatic force) that will move one membrane into contact with the other such that the permeability of the structure to gas, vapor, liquid and/or particulates is decreased. However, a structure such as that disclosed may be subjected to use for the purpose of protecting against exposure to extremely toxic agents, such as those encountered in chemical and biological warfare.
It may thus be desirable in such situations to consider an alternative to disclosed structure. Such an alternative may incorporate additional barrier(s) to the transport of threatening agents that cooperate with the movable membranes of the adaptive membrane structure as described, and thereby limit the permeability of the structure to threatening agent(s), even in the event of an incomplete seal between the movable membranes. Furthermore, such hybridization of an adaptive membrane structure with additional barrier(s) when properly designed will result in enhanced performance of these additional barrier(s) in rejecting threatening agents relative to their performance without such hybridization.